1. Field of the Invention
The present invention relates to a method for manufacturing a polarizer, and to a polarizer obtained by the method. And, this invention relates to a polarizing plate using the polarizer and an optical film, and furthermore to an image display, such as a liquid crystal display, an organic electroluminescence display, a PDP, and the like, using the polarizing plate and the optical film. Furthermore, this invention relates to a wet type stretching apparatus having a treatment bath used for wet type stretching processing in the method for manufacturing a polarizer.
2. Description of the Prior Art
Liquid crystal display (LCD) are used for personal computers, TVs, monitors, cellular phones, PDAs, etc., and in such fields, colorization, reflective colorization and high definition, and high brightness are promptly realized in recent years. In order to realize these expansions of application for LCDs and improvement in display qualities, such as high definition and raise in brightness, performance upgrading of polarizing plates used for LCDs in optical characteristics (improvement in transmission factor or polarization degree) is required.
Since it has high transmission factors and high polarization degrees, polyvinyl alcohol based films treated with dyeing treatment have been conventionally used as polarizers used for liquid crystal display devices etc. Besides, the polarizers are usually used as polarizing plates with protection films attached on one side or both sides thereof. In recent years, more advanced performances are required for liquid crystal display devices, and higher transmission factors and higher polarization degrees are required also for polarizers, and as a result, various methods for manufacturing polarizers that can be adapted to such requirements are proposed.
As a method for performance upgrading of the optical characteristics of the polarizers, a method giving high ratio stretch processing of polyvinyl alcohol based films in manufacturing process of polarizers may be mentioned. Stretching at high ratio given to polyvinyl alcohol based films, however, provides high possibility of outbreak of so-called “breakage at the time of stretching”, that is, fracture of films under stretching, which is not preferable in productivity. Moreover, a stretching method performed in two or more steps of a polyvinyl alcohol based films may be mentioned. However, larger stretching ratios after a second step easily give the above-mentioned “breakage at the time of stretching”, and as a result polarizers having high polarization degree may not be stably obtained.
The present invention aims at providing a method that may stably manufacture a polarizer comprising polyvinyl alcohol based films stretched at high stretching ratios. This invention also aims at providing a polarizer obtained by the manufacturing method, and further aims at providing a polarizing plate and an optical film using the polarizer. Furthermore, this invention aims at providing image display using the polarizing plates and the optical films, and furthermore, this invention relates to a wet type stretching apparatus having a treatment bath used for wet type stretching processing in the method for manufacturing a polarizer.